This invention relates to metal containers, particularly cylindrical metal containers with relatively large holding capacities, such as steel drums, made by fastening end plates to both ends of a cylindrical body by seaming, and the method of manufacturing and the apparatus therefor.
The description in this specification will refer to steel drums as a typical example of such metal containers.
A steel drum is made by fastening a round end plate to each end of a cylindrical body. The fastening is generally accomplished by laying together the flanges at each end of the body and around the circumference of the end plate and then bending them over in folds. During the forming process, a sealing compound is applied between the folds or in the seam to prevent the leakage of drum contents therethrough.
In forming the seam, a tray-like end plate is first fitted in both ends of a cylindrical can body, each end having a flange extending perpendicular to the longitudinal axis of the body. A seaming chuck having a cylindrical forming face is fitted in the end plates, which are then held, and turned around the can body axis along the can body. A seaming roll having a forming groove is pressed against the forming face of the seaming chuck, with the edges of the flanges on the body and end plates held in the forming groove. Consequently, the flange edges are guided along the side and bottom of the forming groove and thereby become folded and seamed together. Then, the seam is pressed and the shape corrected between the seaming roll and the forming face of the seaming chuck, thereby attaining a closer contact between the flanges.
The drum seam thus formed has an important bearing on the quality of the drum, including its strength and leakage proofness. Formed along the outer edges of the drum, the seam is likely to strike against other objects when the drum is raised or lowered or during transportation, which will probably cause the deformation, loosening and cracking of the seam. This leads to leakage. To avoid such deformation, loosening and cracking of the seam, many proposals have been put forward and implemented with respect to the structure of the seam and the method and apparatus for making the seam.
For example, structures of the seam are disclosed in U.S. Pat. Nos. 3,736,893 and 3,987,927.
The seam according to U.S. Pat. No. 3,763,893 is formed by helically wrapping the flanges of the body and end plate which have been laid one over the other. Having a round cross-section, this seam, it is claimed, develops a large moment of inertia and, therefore, a great strength in the direction of its radius. In this seam, however, the flanges of the body and end plate are held in contact with each other simply as a result of enfolding. In addition, this seam has a relatively large void in the center, so that a filler must be put in the void to insure adequate leakage-proofness. This use of the sealing compound not only entails an increase in production cost, but also involves a risk of degenerating the contents of the drum that may possibly come in contact therewith.
The seam according to U.S. Pat. No. 3,987,927 has an egg-like or elliptical cross section, with a relatively small radius of curvature at the top of the seam (where the first fold is made). The strength at the seam top is increased because of the work hardening resulting from the reduced radius of curvature. This, however, is likely to cause excess deformation of the seam, which, in turn, may lead to cracking. If no great pressure is applied to the seam in the final stage of the seaming process, the contact between the hooked edges in the center of the seam is less close than when great pressure is applied. If sufficient force is supplied to sufficiently tighten the seam, the pressed part may develop cracks because of work hardening.
A method and apparatus for making drums, particularly those for forming drum seams, are required to provide seams with high leakage-proofness and strength in an easy and sure manner. Recently, furthermore, the demand for drums make of lighter-guage steel sheets has increased. To provide greater strength, the use of a triple seam is popular in this type of drums.